In multi-phase electronic converter applications, a number of bridge driver circuits (full or half) can be cascaded together while sharing a common power supply 110. A full bridge converter 100 is shown in FIG. 1 with four actuators (120) cascaded together. In this design, each load element 120 (actuator) is independently controlled by modulating the conduction of the appropriate power devices, in one of the three voltage operating modes (positive voltage, negative voltage, free-wheeling mode) by actuating switches 112 and 118, 114 and 116, 112 and 116 or 114 and 118, respectively.
A half-bridge equivalent configuration can also be used for applications that do not require bi-directional current flow, shown in FIG. 2. One difference between the two is that the half bridge circuit 200 has two of the power switches (114 and 116) replaced with power diodes (122 and 124, respectively). This substitution provides a cost reduction by eliminating the power switches as well as the associated gate drive circuitry and controller complexity.
Either type of converter can be used for controlling actuators and are representative of the majority of power converters that can be used.
However, the inventors herein have recognized a disadvantage when trying to use such converter designs to control electromechanically actuated valves of a cylinder in an internal combustion engine. For example, in the case of a half bridge converter, four power devices (2 switches and 2 diodes) are required for each electromagnet. And, since electrically actuated valves of an engine typically use two actuator coils per cylinder, a typical 32 valve V-8 engine would require 256 devices. This creates a significant added cost for an engine with electromechanically actuated valves, even if not all valves are electrically powered. Further, not only would the above converter approaches require significant numbers of devices, but would also increase wiring and harness costs, since two wires are required per actuator coil.